1. Field of the Invention
The present invention is directed to a pressure pulse source having a positive lens for focusing the pressure pulses onto a focal zone, and having at least one pressure sensor containing a piezoelectric polymer foil applied to the surface of the positive lens which forms the sound exit face.
2. Description of the Prior Art
A pressure pulse source is disclosed in European Application 0 229 981 having a plurality of pressure sensors arranged on the sound exit face of a positive lens which focuses the pressure pulses onto a focal zone. The pressure sensors identify properties of the focal zone, such as the dimensions thereof, particularly during operation of the pressure pulse source. The measured values supplied by the pressure sensors are compared to rated (desired) values which correspond to a focal zone having defined dimensions. Other important information which may be useful in the operation of the pressure pulse source, however cannot be acquired using this known pressure pulse source, or cannot be acquired with adequate precision. Such information includes, for example, information about the chronological curve of the pressure pulse and the peak value of the pressure of the pressure pulse emerging from the positive lens. Such information also includes information as to whether the pressure pulse source is aligned relative to a subject to be acoustically irradiated so that the subject, or a defined region of the subject, is situated in the focal zone.
Particularly given utilization of a pressure pulse source for medical purposes, for example for non-invasive disintegration of calculi, information of this type is of basic significance for the safety of the patient, and thus such information must be constantly available during operation of the pressure pulse source. Knowledge of the chronological curve of the pressure of the pressure pulse emerging from the positive lens permits exact conclusions to be drawn regarding the peak pressure to be anticipated in the focal zone, which should not be any higher than absolutely necessary in order to avoid unnecessary tissue damage. Moreover, the region to be acoustically irradiated should always be precisely situated in the focal zone of the pressure pulses, so as to avoid unnecessary damage to surrounding tissue.